Often Special:Log/newusers is watched for abusive usernames. It'd be nice if blocks where already displayed in the log, as for now you have to click "block" just to find out someone else already blocked the user.
I think this should be doable by doing a left outer join ipblocks on ipb_user=log_user. Werdna suggested to add a ipb_expiry check just to make sure the information is up to date.